The present invention relates to a thrust recovery valve and more particularly, to a thrust recovery valve having two flaps, with each flap controlled independently via its own actuator. The present invention further relates to a cabin pressure control system that includes one or two thrust recovery valves.
Aircraft which utilize conventional thrust recovery valves, or other skin mounted cabin air exhaust valves, face several challenges in their design and performance.
The first challenge is that there are times when a high resolution of control is required during flight at high differential pressures across the fuselage. The high resolution is required because the control of cabin pressure requires very small valve aperture changes for each periodic valve adjustment.
The second challenge is that the aerodynamic torque on the valve can be very great when the valve is opened because the frontal area of the valve is in the slipstream of air passing by the valve.
Another challenge is how to optimize ram air ingress of air from outside the airplane during negative pressure relief operation. Traditionally, the thrust recovery valve can only open to a 90-degree position with both doors linked (or on a single door valve, the single door opens to 90-degrees) and an external suction is created after the first (or only) door position such that a lot of air exits the fuselage into this lower pressure region—overcoming the benefit of the rammed in air prior to the forward door. Therefore, on some airplanes, a dedicated ram air scoop is used to provide for ventilation airflow during negative pressure relief conditions. This ram air scoop adds system weight and complexity and cost.
An additional challenge is that thrust recovery valves are expensive and heavy, so having more than two thrust recovery valves can be wasteful. But, in the event of a mechanical failure of the valve, having two or one thrust recovery valves can limit the ability to dispatch the airplane with one thrust recovery valve “blocked” closed, since air distribution and positive and negative pressure relief functions are compromised (higher probability that after the failure of the remaining valve a hazardous event could occur).
Finally, thrust recovery valves may be operated via rotary actuators, with linkages to both doors, such that the structure to hold the actuators often drives the weight of the thrust recovery valves higher than desired.
It is possible that each door of the valve might need to be operated by independent controls, sometimes working together to accomplish the same goal (ground opening for ventilation) and sometimes each having different functions (regulating differential pressure in flight on one control while providing various ventilation functions with the other).
U.S. Pat. No. 6,273,136 describes a thrust recovery valve design utilizing one “common” “drive mechanism” for both valve (stages) doors, using complex linkages and door arrangements to accomplish some of the above stated advantages. Further, the prior art, has a one drive mechanism controller to drive the common drive mechanism that actuates the multiple stages of the valve.
As can be seen, there is a need for a thrust recovery valve that may provide failsafe operation and reduce weight, complexity and cost while providing cabin air pressure regulation within the aircraft.